1. Field of the Invention
The present invention relates to an internal combustion engine cylinder head, and particularly to a cylinder head having induction hardened surfaces surrounding the through holes that receive fastener bolts for fastening the head to the engine block.
Typically, an internal combustion engine will include an engine block and a cylinder head secured to said block by plural fastener bolts extending through the block into threaded openings in the block. Each fastener bolt has an enlarged head in facial engagement with an annular machined surface on the cylinder head, whereby the cylinder head is prevented from separating from the block.
During engine operation, the combustion process generates pressures that tend to cyclically increase the thermal and mechanical forces between the annular machined surfaces on the cylinder head and the bolt surfaces along the firedeck face. Also, high temperatures associated with the combustion process tend to thermally expand the cylinder head and block so as to increase the contact forces between the annular machined surfaces and the bolted joint.
In some cases, the high thermal/mechanical forces exerted the bolt hole surfaces on the head produce small cracks on the machined surfaces. The present invention relates to cylinder head construction designed to eliminate or substantially reduce the objectionable cracking on the head machined surfaces. The present invention greatly reduces the effects of thermally induced stress at the cylinder head outside diameter at the bolt holes sufficient to cause cracking.
The cylinder head of the present invention is manufactured by a process that includes the step of induction hardening the annular machined surface in contact with the integral seal that is used to secure the cylinder head to the engine block. The induction hardened surfaces are resistant to cracking or deformation under stresses imposed thereon thermally by cyclic stress.
It is believed that various engine surfaces have been induction hardened to achieve increased wear resistance and fatigue strength. However, fastener bolt-engagement surfaces on the cylinder head have apparently not been induction hardened for the purposes herein contemplated.
2. Description of the Related Art
Cachat, U.S. Pat. No. 4,438,310, discloses a method and apparatus for induction hardening the surfaces of cylinder valves on internal combustion engines. The apparatus comprises an induction coil having a flat frusto-conical surface adapted to be moved into close proximity to a conical valve seat surface. An alternating current is applied to the coil to generate a localized magnetic flux that inductively heats the valve seat.
Hayashi et al., U.S. Pat. No. 4,695,395, discloses heat treating selected surface areas on an aluminum alloy cylinder head. A laser energy source is passed across selected regions of the cylinder head to heat the affected regions to a molten condition. The motion speed of the laser is such that the molten areas rapidly resolidify to a densified condition after passage of the laser. The resolidificaiton process removes casting defects (e.g. pin holes and blow holes from the aluminum casting.
Wakasa, U.S. Pat. No. 4,530,323, discloses a cylinder head having fastener bolt holes formed in upstanding circular bosses integral with the head. Special reinforcing walls and ribs interconnect selected ones of the bosses to prevent the cylinder head from warping away from the block so as to degrade engine performance.